Elongated stopper device

ABSTRACT

The invention relates to an elongated stopper device for flow control of molten metal, i.e., for controlling the flow of molten metal from a metallurgical vessel, such as a tundish.

The invention relates to an elongated stopper device for flow control ofmolten metal, i.e. for controlling the flow of molten metal from ametallurgical vessel, such as a tundish.

It is well known in steel casting to employ a one-piece refractorystopper rod, which is moved vertically by the use of a lifting mechanismin order to vary the cross-sectional area of an outlet opening of thecorresponding metallurgical vessel.

Those stopper rods have also been used to introduce an inert gas, suchas argon, into the molten steel for removing non-metallic inclusionsfrom the molten metal.

In all cases the stopper device must withstand hours submerged in moltenmetal. It must also be capable of enduring the harsh thermal shockencountered on the start-up of casting and any mechanical forces imposedto it.

Insofar many attempts have been made to improve the mechanical andthermal properties of such a stopper device and to improve its behaviourduring use.

EP 0 358 535 B2 discloses a one-piece refractory stopper rod adapted toa lifting mechanism, comprising an elongated stopper rod body of arefractory material, which body being provided with a bore hole, havinga longitudinal axis and extending from an upper surface of said bodydownwardly. Within said axial bore hole a metal bushing is inserted tothreadably receive a threaded part of a metal rod, inserted in saidrefractory body for attachment to a corresponding lifting mechanism.

One problem with such device is the anchorage of said metal bushing withthe refractory material of the body and the requirement to avoiddifferential stresses between the ceramic body and the metal bushinginsert, which can cause mechanical breakage of the ceramic materialduring service operation.

According to DE 198 23 990 C2 a stopper device is disclosed, providingan upper part of the bore hole embodying a ceramic insert. This insertprovides an inner thread, corresponding to an outer thread of acorresponding metal rod threadably fixed within said insert afterinsertion of the rod into said threaded insert. Whilst the use of twoceramic materials reduces the risk of differential stresses between thebody material and the holding insert problems remain associated with thedifficulty in maintaining an accurate threadform in a high strengthceramic material at an acceptable cost.

It is therefore an object of the present invention to provide anelongated stopper device for flow control of a molten metal from avessel, containing molten metal, which is easy to produce and providessimple fixing means for attachment of a corresponding metal rod within acorresponding refractory ceramic body.

It has now been found that such attachment of the metal rod within acorresponding bore hole of the refractory ceramic body may be achievedwith much simpler means than a cylindrical metal bushing or an elongatedcylindrical ceramic insert, namely by at least one anchor such as asheet like part of a different material (compared with the material ofthe body), whereby said anchor is fixed within said body between theupper surface of said body and a lower end of the corresponding borehole and protrudes radially into said bore hole with its main surfacesrunning predominantly perpendicular to the longitudinal axis of the borehole within the upper part of the body.

Contrary to prior art constructions, which disclose fixing means for themetallic rod, said known fixing means all extending along a significantlength of the longitudinal axis of the elongated refractory body, theinvention provides a fixing means arranged predominantly perpendicularto the longitudinal axis of said body and/or said bore hole respectivelyand at a specific position along the length of the bore within saidbody. Insofar these fixing means are much smaller than a bushing, i.e.much less different material is introduced into the ceramic body andmuch less thermal and mechanical stresses between fixing means (anchor)and ceramic body are to be expected.

In other words: The said anchor is arranged at a specific height of saidelongated stopper device at a distance to its upper surface and at adistance to its lower end. Typically it is arranged at a place between10 and 40% of the total length of the stopper device, calculated fromthe upper end of the refractory body, which may be 5-25 cm, typicallyabout 10 cm from the upper end.

Obviously such a generally radial fixing means presents a significantlyreduced axial length than any insert or bushing extending along thelongitudinal axis of a stopper. Any mechanical stresses generated in theceramic body by the longitudinal thermal expansion effects arising fromsaid generally radial fixing means are therefore much lower than thosegenerated with prior art constructions.

Further it may easily be fixed within the ceramic refractorysurroundings (refractory body material), for example during isostaticpressing of said stopper device.

The manufacturing may be done as follows: The aforementioned anchor(s),for example sheet like part(s) is (are) placed with their end portionlocated into corresponding slits of a suitable mandrel (core rod). Arubber outer mould is placed over the mandrel assembly and a refractoryceramic material is filled into the cylindrical space between themandrel and mould. Thereafter the mould containing the refractorymaterial, including the fixing means, is isostatically pressed. Theouter mould is then removed and the mandrel, made of at least twolongitudinally running parts, is removed from the compacted productleaving the outer portion(s) of the anchor(s) (sheet like parts) firmlyembedded in the ceramic body with their inner extremity(ies) projectinginto predetermined position(s) within the ceramic bore.

During said manufacturing a sealing member may further be placed withinsaid mould, as will be described later.

In its most general embodiment the invention relates to an elongatedstopper device for flow-control of molten metal from a vessel,containing molten metal, said device comprising:

-   -   a body made of a refractory ceramic material,    -   a bore hole, having a longitudinal axis and extending from an        upper surface of said body downwardly,    -   said bore hole being equipped along its length with at least one        anchor of a different material, fixed within said body between        the upper surface of said body and a lower end of said bore hole        and projection radially into said bore hole with its main        surfaces running predominantly perpendicular to the longitudinal        axis of the bore hole,    -   said anchor being adapted to receive and fix one threaded end of        a metal rod, inserted into said bore hole.

According to an embodiment said metal rod has an at least partiallythreaded section at its inserted end. This threaded section serves,together with the anchor (fixing means) for attachment of said metal rodwithin said bore hole of said refractory body.

It will be sufficient to achieve said attachment by providing just oneanchor, like a sheet like part, projecting radially into said bore hole.During insertion of the rod into the bore hole the threaded section ofthe rod will run along said fixing part and provide the necessaryattachment of said rod within said body.

Obviously this fixing (anchoring) means should best have a certaincircumferential length. It may extend over 20 to ≦360° of the inner wallof said bore hole or even a bit more.

Especially in cases where it extends over more than 20° it will beadvantageous to arrange said sheet like part with a certain declination(descending gradient or slope) with respect to the longitudinal axis ofthe bore hole, but not necessary to achieve the desired locking.

This is especially true if the anchor (sheet like part) is more or lessring shaped, i.e. running in the circumferential direction around theinner bore hole surface for more than 180°, especially more than 270° C.and it must be sloped when this part has a length of more than 360°. Asnap ring design is one further possibility.

While said anchor may be designed as a ring, for example with acircumferential length between 270° and ≦360° or up to 450° or 300° to400° it is also possible to prepare said fixing means by at least twoanchors, each designed like a ring section and arranged at a distance toeach other along an imaginary helical line. A further embodimentprovides fixing means made of three anchors, each designed like a ringsection and arranged at equal distances to each other along an imaginaryhelical line. Even two or three radially arranged pins, spaced to eachother, may provide the necessary anchoring means for securing andholding the rod within the body. The anchor(s) may also be arrangedalong a plane, perpendicular to the longitudinal axis of the rod.

It becomes clear from the explanation above that a one piece fixingmeans is the most convenient way for an easy production of said stopperdevice.

Said fixing means may be made of any material, different from thematerial of the refractory body and strong enough to threadably receivethe threaded part of the corresponding metal rod. For example the fixingmeans may be made of metal or special ceramics like silicon nitride,zirconia or alumina.

As explained above a sealing member may be arranged along said bore holeand best adjacent to said fixing means.

This improves the tightness between the ceramic body and the metal rod,especially in cases where said stopper rod is used for introducing a gasinto a metallurgical melt.

A corresponding sealing member (gasket) may be placed upon acorresponding annular sealing surface, provided at a certain height ofthe bore hole. This construction is further disclosed in EP 1 135 227B1, the disclosure of which is insofar referred to here.

Said sealing means may also be arranged along a circumferential wall ofsaid bore hole below or above said fixing part and extending radiallyinto said bore hole and longitudinally along a certain length of saidbore hole and adapted to receive said rod in a threadably manner.

Insofar as in this description reference is made to “above”, “upper”,“lower”, “downwardly”, etc it is referred to the typical use of suchstopper rod, running predominantly vertical.

As described above a sheet like part used for attachment of thecorresponding rod is arranged along a defined longitudinal position ofthe body. Therefore, when introducing the rod, the corresponding outerthread of said rod will protrude downwardly over said fixing means. Thisprotruding part of the threaded rod section is now used to provide aneffective sealing as it will be engraved into said gasket. The materialof the gasket, withstanding high temperatures, thereby penetrates intothe threads and causes a very effective sealing and tightness over thecorresponding lengths of said sealing and said rod respectively.

Said sealing member may have a cylindrical shape. It should protrudeinto the bore hole.

That part of the bore hole, receiving the sealing member, may beconically designed with its smaller part at its lower end.

The rod may then have a smaller width at its part adjacent to saidsealing member compared with its part on top.

The sealing member may be made of any material withstanding hightemperatures as may be present during use of stopper device. Graphite isone of those materials. A possible material is a compressed graphitematerial with a purity >95 weight-% carbon and a density ofapproximately 1,4 g/cm³. The seal may have the form of a preformedcomponent which can be either inserted into the stopper body immediatelyprior to the installation of the steel support rod or co-formed with theceramic body of the stopper rod during the production process.

Alternatively the seal may be created during the fabrication process ofthe stopper by compression of a graphite element comprising eitherexfoliated graphite powder or a coil of a graphite foil, placed aroundthe forming tool (mould) and then surrounded by the ceramic bodymaterial of the stopper during the mould filling process.

It seems clear from the description above that if said stopper device isused for introducing gas the corresponding rod will be equipped with anaxial bore through which the gas is fed. The corresponding bore hole ofthe body will then be provided with at least one opening at its lowerend.

Further details of the invention will be described in the subclaims andthe other application documents.

The invention will now be described with respect to one embodiment whichin no way limits the scope of the claimed stopper device.

The only FIGURE shows schematically an upper part of a stopper device ina partly longitudinal cross sectional view.

The stopper device comprises an elongated refractory body 10 with acentral bore hole 12, positioned coaxially with respect to body 10 andadapted to receive fixedly a metal rod 14 for its attachment to a(non-shown) lifting mechanism.

The bore hole 12 is of more or less cylindrical shape and is runningfrom an upper surface 10 u of the body 10 downwardly (arrow D) andterminating in a (non-shown) opening at a lower end of said body 10.

At a distance d from upper surface 10 u a sheet like metal ring 16 isintegrated in the refractory material of body 10. Said ring projectsradially into said bore hole 12. Main surfaces (upper surface 16 u;lower surface 16 l) are running predominantly perpendicular to alongitudinal axis A of said bore hole 12.

In the FIGURE said flat ring 16 is arranged such that is provides anangle α of ca. 3 degrees to a horizontal plane (perpendicular tolongitudinal axis A). This angle may be adapted to match the pitch ofthe threadform on the metal rod 14. Said ring 16 is not closed but slitand encircles an angle of about 330°. Free ends of said ring are offsetin the longitudinal direction of bore hole 12.

This sheet like ring 16, serving as a fixing means for said rod 14,which will be described later, has been co-pressed with body 10. Itprotrudes (projects) into bore hole 12 over a certain width so as tothreadably receive an outer thread 14 t (symbolized by dots) of a lowerpart 14 l of metal rod 14, which may have a central, longitudinalthrough passage 14 c (symbolized by lines).

During assembling said metal rod 14 is introduced into bore hole 12,thereby turned, so that the outer thread 14 t of rod 14 engages theprotruding part 16 p of ring 16.

Rod 14 is then further introduced into bore hole 12 (downwardly, arrowD) and then engages a cylindrical graphite gasket 18, arranged over alength L in front of an inner wall 12 w of bore hole 12.

During said further introduction of rod 14 into bore hole 12 the gasketmaterial penetrates into spaces of thread 14 t, thereby providingintimate sealing between body 10 and rod 14 all over length L.

According to the FIGURE the final position of rod 14 within bore hole 12is characterized by a small projection of threaded end 14 e past the endof sealing member 18. Alternatively the threaded rod could finish withinthe length of the sealing element.

Upper surface 10 u of body 10 butts on blocking means 20, 22 locatedfixedly on metal rod 14 so that rod 14 may not lengthen opposite toarrow D. Blocking means 20, 22 have a nut-like shape and are preparedwith inner threads, corresponding to thread 14 t of rod 14.

The limited size of said sheet like fixing means (slit ring 16) and itsmostly horizontal (radial) arrangement with respect to the elongatedstopper design guarantees safe fixation of rod 14 in bore hole 12 evenwhen under high thermal load said metallic fixing means and saidmetallic rod will expand equally in a radial direction, with little orno differential expansion in the axial direction.

Together with the downwardly following sealing gasket the describeddesign leads to an improved stopper device which may be used fordifferent purposes, i.a. for feeding a gas along channel 14 c and borehole 12 into a metal melt. The intimate contact between gasket 18 andouter thread 14 t of rod 14 are further responsible for the radialcompression of the sealing element and improved tightness of saiddevice. The expansion of the metallic rod at service temperature servesto further increase the sealing efficiency by maintaining compressiveforces on the seal.

In the longitudinal direction the fixing means should be as small aspossible. It may have a “thickness” of ≦5 mm, ≦3 mm, ≦2 mm or even ≦1mm, while the “length” (L) of said sealing means may be ≧10 mm, ≧20 mm,≧30 mm or ≧40 mm.

The invention includes embodiments with two or more fixing means atdifferent positions along the longitudinal axis of the elongated stopperrod, i.e. the respective fixing means have a distance to each other (inthe longitudinal direction of the bore hole). The distance may be in therange of a few cm or more. These distinct fixing means may coact withone or more outer threads of the metallic rod.

1. An elongated stopper device for flow-control of molten metal from avessel, containing molten metal, said device comprising: a) a body (10)made of a refractory ceramic material, b) a bore hole (12), having alongitudinal axis (A) and extending from an upper surface (10 u) of saidbody downwardly, c) said bore hole (12) being equipped along its lengthwith at least one anchor (16) of a different material, fixed within saidbody (10) between the upper surface (10 u) of said body (10) and a lowerend of said bore hole (12) and projecting radially into said bore holewith its main surfaces (16 u, 16 l) running predominantly perpendicularto the longitudinal axis (A) of the bore hole (12), d) said anchor (16)being adapted to receive and fix one threaded end (14 l) of a metal rod(14), inserted into said bore hole (12).
 2. Stopper device according toclaim 1, wherein said metal rod (14) has an at least partially threadedsection (14 l) at its inserted end.
 3. Stopper device according to claim1, including a sealing member (18) being arranged adjacent to saidanchor (16).
 4. Stopper device according to claim 3, wherein saidsealing member (18) being arranged along a circumferential wall (12 u)of said bore hole (12) below said part (16), extending radially intosaid bore hole and longitudinally along a certain length (L) of saidbore hole (12) and adapted to receive said rod (14) in a threadablymanner.
 5. Stopper device according to claim 3, wherein said sealingmember (18) has a cylindrical shape.
 6. Stopper device according toclaim 3, wherein that part of the bore hole (12) receiving the sealingmember (18) is conically designed with its smaller part at its lowerend.
 7. Stopper device according to claim 3, wherein said rod (14) has asmaller width at its part which first enters said sealing member (18)than at its part on top.
 8. Stopper device according to claim 3, whereinsaid sealing member (18) is made of graphite.
 9. Stopper deviceaccording to claim 1, wherein said anchor (16) has a sheet like shapewith its main surfaces (16 u, 16 l) running predominantly perpendicularto the longitudinal axis (A) of the bore hole (12).
 10. Stopper deviceaccording to claim 1, wherein said anchor (16) is made of at least twosheets each designed like a ring section and arranged at a distance toeach other along an imaginary helical line.
 11. Stopper device accordingto claim 1, wherein said anchor (16) is made of three sheets eachdesigned like a ring section and arranged at equal distances to eachother along an imaginary helical line.
 12. Stopper device according toclaim 1, wherein said anchor (16) is a snap ring.
 13. Stopper deviceaccording to claim 12, wherein said snap ring encircles more than 180°.14. Stopper device according to claim 12, wherein said snap ringencircles less than 360°.
 15. Stopper device according to claim 12,wherein said snap ring encircles 360°.
 16. Stopper device according toclaim 12, wherein said snap ring encircles more than 360°.
 17. Stopperdevice according to claim 12, wherein said snap ring encircles less than450°
 18. Stopper device according to claim 1, wherein said anchor (16)is made of metal.
 19. Stopper device according to claim 1, wherein saidrod (14) has an axial bore (14 c).
 20. Stopper device according to claim1, wherein the anchor(s) (16) are arranged at an angle α of between 1and 5° with respect to a plane perpendicular to the longitudinal axis(A) of the bore hole (12).